Some waste materials, originating from electric and electronic equipment and devices (WEEE—waste electric and electronic equipment), for example printed circuit boards, integrated circuits, microchips, memory modules and other parts of electronic scrap have complicated composite structure, which presents a significant problem from the point of view of treating such waste material. Such composite waste materials contain valuable materials integrated with troublesome and dangerous substances in close proximity and must be processed separately for utilization or disposal. Nonferrous metals like copper, tin or lead, constitute a valuable component of electronic scrap, the content of these metals reaching up to 35% of the scrap weight. The electronic scrap often contains also noble metals, in particular silver, gold, platinum and palladium, wherein the noble metal content in some types of “high grade” integrated circuits may reach up to 0.3%.
On the other hand, complicated kinds of electric and electronic scrap often comprise troublesome and dangerous substances. Ceramics and plastics represent further components, constituting the waste, and they represent about 60% of their weight. The printed circuit boards, reinforced with glass fibers, often contain halogens, especially bromine, as a component of retardants of plastics and resins combustion. Nonseparated conductors are often isolated by PVC. In some waste materials of the electronic scrap it is possible to identify integrated capacitors, containing PCB (polychlorinated biphenyls). It is obvious that thermal treatment of such waste by standard metallurgical methods in the presence of air oxygen creates a risk of forming dioxins and furans, as well as other dangerous substances. Therefore, because of ecological, but also of economical reasons the metals as well as other valuable components of the composite waste must be separated to a high degree of purity before further utilization, what can be achieved only by extensive disintegration.
A good electronic scrap and composite waste recycling method must allow for separation of individual components in such a way that the obtained metals would contain minimum of non-metallic components and, simultaneously, it must allow recycling also for the organic fractions, especially plastics. From a pure mixture of nonferrous metals it is subsequently possible to obtain by standard metallurgical methods not only the prevailing metal-copper, but also other metals, like zinc, lead, tin, as well as silver, gold, platinum and palladium.
The presently known methods and techniques of treating and recycling multicomponent parts of waste electric and electronic devices and equipments which fulfill the above given criterion, can hardly be accepted from the ecological point of view, or they are economically highly demanding.
The most spread recent techniques of recycling composite and combined electronic scrap are based on physical, especially mechanical principles. The first stage of recycling consists usually of manual dismantling the device or apparatus and detaching simple parts. To eliminate contamination of the other components, it is necessary to remove from the composite parts, especially from the printed circuit boards, batteries containing heavy metals (nickel, cadmium), mercury switches, and PCB containing capacitors. This step is sometimes omitted or it is infeasible because of the component size. The waste composite material is subsequently mechanically disintegrated in several steps, usually in two- to four-rotor crushers, cutters and hammer mills, possibly in granulating machines. Metal iron is separated from the crushed material by a magnetic separator. The obtained crushed material without iron is subsequently sorted with the aim to separate the other metals from the remainder using various physical procedures. Vibrational sorting machine, sorting in air stream or electrostatic separators are often used. Some valuable individual components are separated from the remainder by flotation or similar methods utilizing the differences in density of the involved components and gravitation.
The products of mechanical recycling consist usually on one hand of concentrates of iron and nonferrous metals including undesired content of residua and organic substances, subsequent treating of which by metallurgical techniques is accompanied by adverse ecological consequences. On the other hand the products of such recycling are predominantly a non-metallic remainder and dust, which, as a consequence of their composition and content of residua, represent nonutilizable waste. The yield of metal recycling using the above classical procedures is limited and, moreover, a part of the noble metals becomes a part of waste, often dangerous, which makes up to 60% of the original waste composite material. Recycling of organic substances, especially macromolecular substances from composite electric and electronic waste do not belong to the worldwide background art.
Procedure, described by F. Ambrose and B. W. Dunning in the work “Accomplishments in Waste Utilization”, 7th Mineral Waste Utilization Symposium, Chicago, Oct. 20-21, 1980, Washington, US Department of the Interior, Bureau of Mines, is oriented at recycling military electronic scrap in the form of complete, undismantled switch boxes, as well as individual circuit boards. The waste is disintegrated in several stages in various devices and equipments and after each disintegration stage particles of the corresponding material are separated. Iron particles are separated magnetically and aluminum particles are separated in an eddy current separator. A cylindrical electrostatic separator may be used for treating a mixture of smaller metal particles and non-conducting residua. The final products of this treating procedure are iron, copper, aluminum, further metals and contaminated remainder, containing unseparated metals and residua. The metals may be, if necessary, refined or used directly as a starting raw material. The noble metals may be recovered by hydrometallurgical processes in specialized metal refineries. The residue cannot be usually utilized anymore and it must be treated as dangerous waste.
According to the method, described by K. O. Tillman in the work “Recycling betrieblicher Abfälle” (“Recycling industrial waste”), loose-leaf edition, July 1991, WEKA Fachverlag Kissingen 1990, isolated printed circuit boards, that have been detached from the devices, are first crushed in a two-rotor cutter crusher to particles less than 30 mm. Iron particles are removed from the resulting mixture using a magnetic separator. The remainder is cooled with liquid nitrogen to a temperature of −130° C., at which the plastic fractions become fragile. The cooled waste is ground in a continually working hammer mill and disintegrated to fine particles. The granulate is separated in a vibrational separator to a metal and a remainder fraction. The powder residue is accumulated and sent to a refinery for recovery of noble metals present. In a specialized metallurgical plant, copper is recovered, and the rare metals, present in the metal fraction, obtained in the anode mud after copper recovery, may be treated in a refinery for rare noble metals. The remaining fractions are not utilizable as raw material.
The above given methods do not ensure sufficient disintegration of the composite material and, moreover, the commonly used separation devices do not achieve sufficient level of separation. A consequence of this is that the metal fraction still contains a relatively high portion of residual materials, among others also halogens, what leads to formation of dioxins and furans during melting of metals. This reduces advantages of metal recycling from waste.
Moreover, the remainder fractions, considered to be waste, still contain 10 to 20% of metals, which fact may in case of waste thermal treating adversely influence the lifetime of the catalyst used for treatment of combustion gases.
Some disadvantages of the above procedures are eliminated by the methods described in the patent documents U.S. Pat. No. 5,683,040 and U.S. Pat. No. 6,244,054. These methods utilize, as the key operation of disintegration of composite materials, cryogenic treatment of the composite material, from which batteries, switches and capacitors, which contain harmful substances, are removed before the cryogenic treatment, and the material is ground to smaller particles. Liquid nitrogen is used as the cryogenic substance. Embrittled overcooled particles are discontinuously ground in a hammer mill, where the ground material is simultaneously separated on sieves into a fine and a coarse fraction. Coarse metallic fraction can be discontinuously taken away from the device. Of this fraction iron can be separated in a magnetic separator. The fine fraction is sorted based on the particle size into several narrow subfractions, which may be independently separated in a corona-roller separator in metallic and residual non-metallic particles. In the procedure, described in U.S. Pat. No. 6,244,054, supercooling the composite material in a cooling tank is optimized by adding it in discrete doses and by discontinuous withdrawing the supercooled material for grinding, whereby optimization of the liquid gas consumption, reduction in energy consumption, minimization of necessary human labor and working time are achieved.
Although the latter procedures yield metal concentrates of high purity, residual fractions with low content of metals, and they minimize emissions from the recycling process, they have a disadvantage that, in consequence of energy demandingness of cryogenic techniques, they approach the limits of economical acceptation because of high operation costs. Moreover, they do not allow utilization and recycling of non-metallic residua, especially organic fractions present in the composite materials.
Also known is the method of treating low-grade organic substances according to the SK patent No. 279 397, the nature of which consists in that the low-grade organic substances are subjected, at a temperature of 150° C. to 700° C. and at a pressure of 0.1 MPa to 2.5 MPa, to the action of a moving bed of solid particles which perform whirling motion, whereby the solid particles of a substance constituting the moving bed are set in whirling motion by intensive stirring.
The aim of the present invention is to eliminate disadvantages of the methods used so far, especially of the methods of recycling electric and electronic scrap, in which the key operation is disintegration of composite material.